Art of drying coal in the mill



May 27, 193.0. H. KRElslNGER 1,760,148

ART OF DRYING COAL IN THE MILL Filed Aug. ll, 1928 x I I I 1 I l l l I l I 1 l Patented May 27, 1930 UNITEDv STATES 4Pm'srr OFFICE HENRY KREISINGER, OE PIERMONT, NEW YORK, ASSIGNOR TO INTERNATIONAL OOM- BUSTION ENGINEERING CORPORATION, OF NEW YORK, N. Y., A CORPORATION OF DELAWARE ART OE DRYING COAL IN THE MILL application mea August 11, 192s. seriai No. 299,091.

This invention relates to the art of drying coal and particularly to the drying of coal ration and handling of coal to be burned in pulverized fuel burning furnaces.

It is customary in preparing coal for pulverized fuel burning installations to dry the crushed coal before pulverization as by means of special driers which not only are of considerable cost but also are expensive to maintain. Recently drying in the mill has also been resorted to, but certain difficulties as will hereinafter appear have been encountered.

The primaryobject of my invention is to provide a method and apparatus whereby I am enabled to eii'ectively dry the coal in the pulverizing mill and thus provide a great ly simplied coal preparing device.

Another obj ect of my invention is the provision of a mill adapted to dry the coal as well as pulverizing it in which danger of lires in the mill is guarded against.

A further object of my vinvention is the provision of a mill having capacity to dry the material to be pulverized therein in which the heating medium is introduced in a novel manner.

- How the foregoing together with such other objects and advantages as may hereinafter appear, or are incident to my invention,

are realized as illustrated in preferred form in the accompanying drawing, wherein:

The figure is a partial vertical section and partial elevational view of a device embodying my invention.

In the drawing the mill as a whole is designated by the reference character A and is provided with feeding mechanism 2 of any suitable form to which the material, in this instance crushed coal, is fed from a storage bin by means of the spout or pipe 3. The feeder vmechanism operatesto 'feed coal in lproper quantities to the grinding chamber 4 where itis caught by plows 5 and thrown up `for pulverization by suitable grinding mechanism which in the type of mill illustrated comprises a plurality of grinding rollers 6,

and a bull ring 7. The plows are preferably l located one just ahead of each roller.

Air separation mechanism B is associated with the mill A for separating the finely ground material from the coarser particles which mechanism comprises a cyclone separator 8, a fan 9, a pipe 10 leading from the i top of the mill to the suction side of the fan, a pipe 11 leading from the discharge side of the fan to separator 8, which pipe is arranged to tangentially discharge into the separator, and a vented return pipe 12 leading from the top of the separator to a casing 13 providing a chamber 14 surrounding the grindin chamber 4. The particular arrangement o the return pipe 12 will be hereinafter described.

A series of openings 15 preferably` tangeni tially arranged are provided around the lower portion of the griigding chamber which `afford communication between the chambers 14 and 4.

From the foregoing it will be seen that a constant lifting stream of air is drawn through the mill by the fan 9, the stream entering the mill-through the openings 15 and passing upwardly around the rollers and bull ring, then into the separator 8 and finally returning from the separator to the chamber 14. In such passage the air carries the finely pulverized material from the grinding chamber to the separator and the coarser and heavier particles fall back into the mill and are thrown up by the plows for regrinding to the desired ineness.

'Io dry the coal I introduce a .heating medium, such` as Hue gas or heated air, or a mixture of the two, intotheI chamber 14 which exerts a drying effect upon the coal in the mill.

I have found that if satisfactory results are to be obtained when drying in the mill the manner of introducing the heating medium into the mill is of importance and unless this is accomplished in the proper mannerdiiliculties will be encountered particularly with res in the mill and therefore/I propose to introduce the `heating medium in a novel manner overcoming the diiiculties.

v In order that the inventlon may be better understood I will, before describing how I overcome the diiiiculties, explain the action which takes place in the mill. There is always a certain amount of-coal pushed out by the plows into the air distributing chamber 14 and into the space between the vanes providing the openings 15. Also a certain amount of coal tends to remain on the upper surface of the memberv 16 of the driving mechanism of the 'mill. to isf usually too coarse to be moved by the current of air back into the grinding chamber and may remain lying at the points mentioned for a considerable period of time until it is either removed orpushed into the grinding chamber bythe operator of the mill. i

Owing to this condition within the mill it has been found that if hot air is introduced into the mill in such manner that it will contact with or strike the stationary coal so collected the coal would become heated and set on lire in consequence of which an explosion in the mill might occur.

I propose therefore to introduce the heated air vinto the mill in such manner that it will not strike or contact with the collected coal and to this end I locate the hot air inlet 17 in such relation to the return air inlet-18 that the cooler air, namely the ret-urn air, sweeps 3e remains stratied, so to speak, above the cool over the collected coal and thatthe hot air air.

Stated' in another way, the air is introduced in two layers, one being relatively cool and the other relatively hot, and th'e cool layer being below the hot layer. By way of example it is pointed out that the temperature of the .air returning from the cyclone does not usually exceed 125 F. while the temperature of the heated air may be as high as 37 5 F. or more.

In the drawing I have illustrated the return pipe 12 as being connected into the casing 14 at the periphery thereof, and the heated air pipe 19 as being connected to the casing at the top thereof. These pipes 12 and 19 are preferably curved as indicated to discharge in the manner indicated by the arrows. v

A 'baiiie 19a may be employed to further ensure the two layers of air abovereferred to. Such a baiiie would be particularly desirable in cases where the pipe 19 is so located that the air enters at right angles to the casing.

While the heated air ultimately comes in Contact. with moving coal to eii'ect the desired drying, it does not come in contact with collected or stationary coal in the bottom portion yof the mill; The moving coal with which the air contacts does not stay in the mill very long, and consequently will not become overheated to start a re or cause an explosion.

An olf-take or vent 20 is provided to compensate for the lintroduction of Hue gas or The coal referredheated air into th'e system and thus moisture laden air is replaced by heated air or gas.

From the foregoing it will be seen that I have provided a mill which can be used as a drier and thus the more complicated drying apparatus ordinarily heretofore employed may be dispensed with and the difficulties mentioned overcome.

I claim 1. In a pulverizing mill of the gas lift type, the combination of the mill casing and its grindingl parts, with means for supplying a lifting current of relatively cool gas, and means for supplying a lifting current of relatively hot gas, said two means being so relatively disposed that the cool gas is interposed lbetween the hot gas and those parts of the mill in which there is a collection of relatively stationary material.

2. Ina pulverizing mill having communicating grinding and gas distributing chambers in which coal collects as an incident to operation of the mill, means for admitting relatively cool gas into the mill and means for admitting a heating medium into the mill, said two means being so relatively disposed that the cool gas and heating medium are in superimposed layers, the layer of cool gas being below the layer of heating medium. y

, 3. In combination, a pulverizing mill having communicating grinding and gas distributin chambers in which coal collects as an inci ent to operation of the mill, means for introducing relatively cool gas into said chambers at the lower portion thereof and in a direction to `sweep over the collected coal,

and means 'for introducing heated gas into said chambers at the upper portion `thereof and in a direction that the heated gas will be prevented from contacting with the collected coalfby the cool gas.

4. In a pulverizing mill the combination with its milling mechanism and its grinding and gas dstributing chambers in which material collects as an incident to operation of the mill, of gas inlets for admitting relatively said casing structure, and means for setting4 Lup a current of such gas thru the mill, the

cool gas and heated gas admitting means being so relatively. located that the cool gas will sweep over the collected coal and that the heated gas will pass thru the casing above the cool gas. 6. In combination, a coal pulverlzing null having a chamber in which coal rejected as an incident to operation of the mill collects, a cyclone separator, a pipe leading from the mill to the separator and provided with a fan, a return pipe leading from the separator v to the chamber of the mill, said pipe being arranged to discharge into said chamber at a point and in a direction that its gaseous contents sweep over the collected coal in the chamber, and means for admitting a hot gaseous medium into said chamber at a point and in a direction with relation to the aforesaid return pipe that the collected coal in said chamber is protected from the heat of the hot gaseous medium by the cooler gaseous medium discharging from they return pipe of the separator.

7. In combination a mill, means for introducing material to be pulverized, a cyclone separator, a pipe leading from the mill to the separator, a return pipe from the separator to the mill, means for setting up a current of lifting gas thru the system, means for venting a predetermined amount of gas from the system, and means for introducing into the system a relatively hot gaseous drying medium in an amount approximating the amount of gas vented from the system, said last mentioned means being so located as to deliver the drying medium at a point above the delivery of the return gas from the separator to the mill.

8. The herein described method of drying material, such as coal, in the pulverizing mill Y which comprises introducing a heated gaseous medium into the upper portion of the mill casing, and introducing a cool gas into the casing below the heating medium so that 'said heated medium remains stratified at a point above abounding wall of the casing where there is a collectlon of relatively stationary material.

In testimony whereof I have hereunto signed my name.

HENRY KREISINGER. 

